Technical Field
The present disclosure relates to a toner, a developer, a toner storage unit, and an image forming apparatus.
Description of the Related Art
A typical image forming apparatus forms an image on a print sheet through the following processes: a charging process in which an image forming area on a surface of an image bearer is uniformly charged; an irradiation process in which a latent image is written on the image bearer; a developing process in which the latent image is developed into a visible image with a triboelectrically-charged toner; and a transfer process in which the image is transferred onto the print sheet either directly or indirectly via an intermediate transferor. After residual toner particles remaining on the image bearer without being transferred are removed in a cleaning process, next image forming process starts.
Demand for high-quality full-color image forming technology is increasing these days. In response to such demand, toner is now required to be much smaller in size for improved thin line reproducibility.
However, small toner particles disadvantageously increase non-electrostatic adhesive force to an electrophotographic photoconductor or intermediate transferor, thus causing hollow defect at thin line portions of the resulting image and/or a decrease of transfer efficiency in the transfer process.
To overcome such a drawback, it has been proposed that toner particles be more spherical in shape, by suppressing the occurrence of micro uneven structure, to decrease the contact area and suppress embedding or rolling of external additives.
However, there arises a problem that the more spherical the toner particles become, the more easily the toner particles pass through a damming member in the cleaning process, thus degrading cleanability. To solve this problem, a technique for improving cleanability has been proposed by making the toner shape irregular and suppressing the irregular-shaped toner particles from passing through the damming member. In view of the above situation, the toner shape is generally designed so as to satisfy both transferability and cleanability in a good balance.
However, even with the toner shape satisfying both transferability and cleanability, it is difficult to achieve stable transferability on sheets with large surface unevenness, although high-quality printing technology on such sheets with large surface unevenness has been demanded recently. In particular, in a situation in which the adhesive force of toner is increased, for example, in a high-temperature high-humidity environment or in a case in which the toner is deteriorated, problems notably occur.